1. Field of the Invention
This disclosure relates to a magnetic random access memory (MRAM) device and more particularly, to an MRAM device for performing a multiple input/output program (write) operation and a multiple input/output repair operation.
2. Description of the Related Art
A magnetic memory cell typically includes a magnetic tunneling junction (MTJ) and a transistor. The MTJ is disposed at the intersection of a digit line and a bit line. The transistor is a typical N channel field-effect transistor.
The typical MTJ having a rectangular shape has a magnetic anisotropy. The MTJ, in general, has a stack structure in which an anti-ferromagnetic layer, a fixed magnetic layer, a tunneling barrier disposed on the fixed magnetic layer, and a free magnetic layer disposed on the tunneling barrier are arranged in that order when viewed from a bottom of the MTJ. The anti-ferromagnetic layer is known as a bottom electrode, and the free magnetic layer is known as an upper electrode. The anti-ferromagnetic layer is connected to a drain electrode of the transistor. The digit line is electrically insulated from the anti-ferromagnetic layer and is disposed under the anti-ferromagnetic layer. The upper electrode or free magnetic layer is connected to the bit line. The fixed magnetic layer has a fixed direction of magnetization that is caused by the anti-ferromagnetic layer. The free magnetic layer is magnetized in a direction according to an externally applied magnetic field generated by the currents flowing in the bit line and the digit line.
Hereinafter, the principle of ‘program (or write)’ operation in the MRAM is described. The magnetization direction of the free magnetic layer is varied in accordance with the magnetic field induced by the currents flowing in the bit line and the digit line. The digit line is substantially perpendicular to the bit line.
The MTJ memory cell has a low (minimum) tunneling resistance value when the fixed magnetic layer has a magnetization direction that is the same as (substantially parallel with) that of the free magnetic layer. In this state, the MTJ memory cell stores data “0” and this state is referred to as “0”-state.
The MTJ has a high (maximum) tunneling resistance value when the respective magnetization directions of the fixed magnetic layer and the free magnetic layer are opposite to (substantially perpendicular with) each other. In this state, the MTJ memory cell stores data “1” and this state is referred to as “1”-state.
Thus, the MTJ has a variable resistance value that is changed depending upon the relative orientations of the magnetization directions of the fixed magnetic layer and the free magnetic layer. The MTJ memory cell is capable of storing 1-bit data (“1” or “0”) according to two magnetization directions of the free magnetic layer.
At the present time, however, an MRAM that effectively performs multiple input/output program (write) operations and multiple input/output repair operations is not available.
Embodiments of the invention address these and other disadvantages of the conventional art.